1. Field of the Invention
The present invention relates to a lens module, and more particularly, to a compact lens module which enables zoom and auto-focus functions even in a small lens module by providing a lens carrying structure using a supersonic driving unit.
2. Description of the Related Art
A camera technique is developed from a film camera using a film to a digital camera which converts an image into digital signals. Recently, such a digital camera is gradually miniaturized and begins to be applied to a personal mobile communication terminal. Quality of the digital camera mounted to the personal mobile communication terminal, for example a cellular phone, is based on the pixel number of the image sensor, which is increasing continually, and nowadays a digital camera having 1 million pixels or more is scheduled for marketing, or already in the market.
The compact camera mounted to the cellular phone is mainly used just for pleasure, but it is expected that the compact camera will be considered as a useful camera beyond its prior function as an amusement tool since an image of 1 million or more pixels is realized recently. Thus, desires for a zoom function and an auto focus function, which are generally adopted in the film camera, are also increased to the compact camera, which may make the compact camera be recognized as a formal camera.
As a semiconductor manufacturing process is applied to an image sensor, it is possible to accumulate more image sensors in a narrow area. However, for the optical zoom and auto-focusing functions, there is needed a lens module design having an especially short stroke and a compact driving unit.
FIG. 1 shows a conventional lens driving structure. FIG. 1 is disclosed in U.S. Pat. No. 6,268,970 in the title of “Zoom Lens Barrel”. In FIG. 1, the barrel includes frames 100 for supporting each lens group 120, 130 and 140, and cam tubes 160 and 170 for supporting the frames. The cam tubes allow the frames to move the lens in an axial direction, and the cam tubes are driven by a driving actuator 110.
In the zoom driving method of such a cam structure, a relative position of each lens is determined according to the shape of the cam while the zoom function is used. Thus, a focusing lens and a driving unit are additionally required for focusing at a specific magnification, and the driving tool becomes disadvantageously complicated and large-sized since a final reduction gear and a lens holding structure moving along the cam are further required.